Conversion of paraffins

ABSTRACT

PARAFFINIC GASOLINE BLENDING COMPONENTS MAY BE UPGRADED BY AROMATIZATION, RECOVERY OF AROMATICS, AND THERMALLY STEAM CRACKING THE REMAINING PARAFFINS TO YIELD AS TOTAL PRODUCT, AN OLEFIN FRACTION AND AN AROMATIC FRACTION.

Aug- 6. 1974 R. F. wlLsoN EVAL CONVERSION OF PRFFINS Filed Deo. 29, 1972 United States Patent O1 tice 3,827,969 Patented Aug. 6, 1974 U.S. Cl. 208-89 10 Claims ABSTRACT OF THE DISCLOSURE Parainic gasoline blending components may be upgraded by aromatization, recovery of aromatics, and thermally steam cracking the remaining paraiiins to yield as total product, an olen fraction and an aromatic fraction.

The novel process of this invention relates to the conversion of paraflins. More particularly, it relates to the production of aromatics and oleiins from a charge parafinic stock.

BACKGROUND OF THE INVENTION As is well known to those skilled in the art, continuing improvements in the quality of gasoline engines, particularly automotive engines, have resulted in the need for better fuels. The octane requirements of the gasolines continue to increase with resultant need for processes which permit recovery of gasoline of increased octane rating. It has always been desirable to upgrade petroleum charge stocks and available refinery streams to permit their use in the gasoline pool; and this need is increasing with the con tinuing demand for high octane lead-free gasolines.

It is an object of this invention to provide a process for preparing gasoline from parafinic charge compositions.

Another object of this invention is to provide a process for.

STATEMENT OF THE INVENTION In accordance with certain of its aspects, the method of this invention for upgrading a charge parainic hydrocarbon may comprise (a) aromatizing said charge parainic hydrocarbon stream in the presence of hydrogen and a noble metal supported catalyst thereby forming an aromatic hydrocarbon stream;

(b) debutanizing said aromatic hydrocarbon stream thereby forming (i) as overhead an unconverted paraiiin stream and (ii) as bottoms an aromatic concentrate;

(c) separating said aromatic concentrate thereby forming (i) a separated paraffin stream and (ii) a separated aromatic stream;

(d) combining said overhead unconverted paraiiin stream and said separated parafn stream thereby forming a combined parain stream;

(e) thermally steam cracking said combined paraiiinic stream thereby forming a thermally cracked combined parain stream; and

(f) recovering said thermally cracked combined paraiin stream.

DESCRIPTION OF THE INVENTION The paraiiinic gasoline blending components which may be treated by the process of this invention may typically be a stream which is available in a renery. Most commonly it will be a stream containing light paraiinic components. Typical of such streams are those containing predominantly lower parains including butanes, pentanes, etc. and illustrative of such streams are light straight run products, various condensates, and rainates from which aromatics have been extracted.

Although the charge may be a pure C4 or C5 parafiin, it more commonly may be a mixture containing C., to C8 parafns. The parailin content may be 60%l00%, preferably 70%-90%, say about 80%. The charge may also contain naphthenes in amount of 5%-30%, preferably 5%-10%, say 8%, and other components such as aromatics in amount of 0%-15%, say 12%. Lesser amounts of other components may be present.

Commonly the octane rating (RON clear) of the charge may be less than about 60, typically 30-50, say 45.

A typical charge stream may be a heavy Udex raffinate (from which the aromatics have been extracted) having the following composition:

TABLE L-UDEX RAFFINATE Percent by volume Component Broad Typical Parans.. 70-90 80.7 Naphthen 5-20 7. 8 Aromatics 2-15 11. 5

Total 100.0

TABLE II.-LIGHT STRAIGHT RUN DISTILLATE Percent by volume Component Broad Typical Paramus sc99 94 Naphthenes 0-18 3. 0 Aromatics 0-15 3. 0

This distillate may have a (RON clear) octane number of 60.8, an IBP of 92F., an EBP of 300 F. and anAPI gravity of 79.2.

These parafnic stocks may be hydrotreated e.g. hydrodesulfurized to remove sulfur compounds and to reduce the content of undesirable metals. Hydrotreating is effected by contacting the charge with hydrotreating catalyst at hydrotreating conditions. Hydrotreating may be carried out at 500 F.850 'F., say 650 F. and 100-3000 p.s.i.g., say 500 p.s.i.g. in the presence of hydrogen in amount of 10G-8000 s.c.f.b., say 5000 s.c.f.b. LHSV may be 0.1-10, say 2. The catalyst may be a Group VIII metal, preferably in combination with a Group VI metal, on an inert carrier; and a preferred catalyst may be that sold under the trademark Aero HDS-3 containing 3.5% Niand 15% Mo on 0.125 alumina. Hydrotreating may decrease the sulfur content from 0.01%-0.4%, say 0.2% to a nal value which may be 0.5-10 ppm., say 1.0 'p.p.m. sulfur.

In the preferred embodiment, the hydrotreated, desulfurized charge paraiinic hydrocarbon in amount of 10,000 b.p.d. may be passed to an aromatizing operation wherein it is contacted with aromatizing catalyst in an aromatizing zone at aromatizing conditions in the presence of hydrogen. Most preferably, aromatizing may be carried out in a reforming operation. Aromatization is effected at 500 F.-1l00 F. preferably 700 F.1000 F., say 950 F. at 0-700 p.s.i.g., preferably 50-500 p.s..g., say 15 p.s.i.g. at a space velocity LHSV of 0.2-5.0, preferably 0.54.0, say 1.0 and a hydrogen gas rate of 500- 10,000 s.c.f.b., preferably G-5000 s.c.f.b. say 5300 s.c.f.b.

Aromatizing caatlyst may be for example a Group VIII metal and a Group VIIB metal on an inert carrier--typi- 3 cally one containing 0.3% Pt and 0.3% Re on alumina such as that sold under the trademark UOP-R-16.

The aromatic hydrocarbon stream exiting the aromatizing operation (after removal of hydrogen which is flashed off and recirculated) may be characterized by the following criteria:

TABLE III Property Broad range Typical API gravity 65-85 S0. 0 R ON clear- 85-100 92. 2 RON (+3 ce.) 90-105 101. l Aromatics, vol. percent 10-50 31.8 Naphthenes, v01. percent. 0-10 1.0 Saturates, vol. percent.-. 21)-80 41. 1 Unsaturates, vol. percent -15 6. 1 Cl, vol. percent 16-25 21. 6 n-Ct, vol. percent 2-5 3. 4. 2MP and 3MP, vol. percent 5-8 6.1 CP, MCP, DMP, vol. percent 2-5 3. 1 n-C1, vol. percent 0-1 0. 2 Benzene, vol percent-. 12-30 19. 4 Toluene, vol percent 5-20 12.3 Orl", vol. percent-.- 1-20 a. 1 Other, vol. percent- 0-10 1. 0 Total 04+, vol. percent 50-90 72. 2 C; to C4, vol. percent -50 36.0

NorE.-MP=Methyl pentane; MCP=Methy1 cyclopentane; DMP: Dimethyl pentane; CP=Cyclopentane.

This aromatic hydrocarbon stream is debutanized to yield (i) an overhead unconverted parainic stream which may normally also contain some olens and (ii) as bottoms an aromatic concentrate.

The overhead unconverted parat-linie stream, recovered in amount of 1000-5000 b.p.d., say 3600 b.p.d. contains mainly light gaseous parains including methane, ethane, propane, and butanes. Lesser amounts of light olens may be present. f

The aromatic concentrate bottoms, recovered from the debutanizing operation in amounts of 5000-9000 b.p.d., say 7220 b.p.d., may be a liquid recovered at 700-1000 F., say 950 F. and 15-500 p.s.i.g., say 50 p.s.i.g.; and it may typically contain primarily benzene and toluene plus parains.

In practice of the process of this invention, the aromatic concentrate bottoms from the debutanizing operation may be passed to an aromatics separation operation which typically may be a sulfolane or a furfural extraction unit (or a molecular sieve separation operation) wherein there may be formed (i) a rafnate stream containing unreactcd parains and (ii) an extract stream containing aromatics.

In typical operation, aromatic separation may be carried out by contacting 2-6 volumes, say 4 volumes of sulfolane solvent per volume of hydrocarbon charge at temperature of 250 F.350 F., say 300 F. and 90160 p.s.i.g., say 120 p.s.i.g. The extract stream, after separation and recovery, may be 10006000 b.p.d., say 3100 b.p.d. of an aromatic stream containing benzene and toluene.

The ranate stream, after separation and recovery may be 2000-6000 b.p.d., say 4100 bpd. of a stream containing unreacted parans characterized by the following criteria:

In the preferred embodiment of the process of this i11- vention, the overhead unconverted parafiinie stream from the debutanizing operation and the raffinate stream from the separation operation containing unreacted parans may be combined to form 3000-9500 b.p.d., say 7700 b.p.d. of a combined parain stream.

This combined paraffin stream is passed to a thermal cracking operation wherein cracking is preferably carried out non-catalytically in a tubular furnace, or oil heater, in the presence of steam. The temperature of thermal steam cracking may be l F.-l700 F., preferably l200 F.-l600 F., say 1400 F. at 0-100 p.s.i.g., preferably 3-50 p.s.i.g., say 25 p.s.i.g. with a steam to hydrocarbon mole ratio of 0.1-10, preferably 0.2-8, say 5.

The thermally cracked product stream typically has the following composition:

TABLE V Composition: Vol. percent Hydrogen 14.5 Methane 28.5 Acetylene 0.4 Ethylene 27.6 Ethane 5.7 Propylene 12.5 Propane 1.8 Butadiene 2.3 Butene 5.3 n-Butane 3.2 i-Butane 0.2 Pentane plus 19.

This stream may be separated in a stripping operation into (i) an olefin-containing cracked combined parain stream as overhead and (ii) a thermally cracked naphtha stream (i.e. a dripolene) as bottoms.

Stripping is preferably carried out in a fractionation operation to which the thermally cracked product stream is admitted. The overhead, an olefin-containing cracked combined paraffin stream, is recovered in amount of 102 volume percent of charge to the thermal cracker.

In practice of the preferred embodiment of the process of this invention, the thermally cracked naphtha stream may be hydrogenated in a hydrogenation operation carried out in the presence of hydrogenating catalyst at hydrogenating conditions to yield a hydrogenated thermally cracked naphtha stream. Hydrogenation is carried out at 300 F.-750 F., say 650 F. at 150-800 psig., say 500 p.s.i.g. in the presence of hydrogen charged in amount of 30D-5000 s.c.f.b., say 1000 s.c.f.b. of charge hydrocarbon. Hydrogenation catalyst may typically comprise a Group VIII metal or compound thereof such as nickel or platinum on a support such as carbon. Preferred is a Group VI and a Group VIII metal, oxide, or sulfide e.g. Ni, Co, Mo, W, and mixtures thereof, more preferably Ni-W or Co-Mo, supported on a refractory inorganic oxide such as alumina, silica, magnesia, zirconia, or mixtures thereof. A preferred catalyst may contain 2% 15% by weight of Group VIII metal and 5%-30% by weight of Group VI metal.

Product hydrogenated, thermally cracked naphtha recovered in amount of l000 2500 b.p.d., say 1430 bpd. may be characterized by the following criteria:

It is an additional feature of the process of this invention that the product hydrogenated thermally cracked naphtha may be passed to a separation operation wherein it may be separated into a paraffin stream and an aromatic stream. In practice of a preferred embodiment, the product hydrogenated thermally cracked naphtha from the hydrogenation operation would be combined with the aromatic concentrate bottoms from the debutanizing operation to form a blended stream to be charged to aromatic separation.

It will be apparent to those skilled in the art that the novel process of this invention permits highly eicient conversion of charge paraffin streams into maximum yield of valuable aromatics and oleiins. Typically without further treatment of stripped thermally cracked naphtha stream, the process may permit conversion of the charge parain stream to give %-60%, say 31% by volume of desired aromatic product.

It will be apparent that the further treatment of the thermally cracked naphtha stream, including hydrogenation and aromatics separation (with preferred recycling of parains to thermal steam cracking) may permit an increase in aromatics.

DESCRIPTION OF PREFERRED EMBODIMENT Practice of the process of this invention will be apparent to those skilled in the art from inspection of the following description wherein, as elsewhere in this speciiication, all parts are parts by volumeunless otherwise specifically set forth.

EXAMPLE I Practice of this invention according to one of its embodiments may be carried out in accordance with the schematic process ow sheet as set forth in the drawing.

Charge to the unit in line 10 may include 10,000 b.p.d. of an Arabian Light Straight Run Naphtha having the properties set forth in the last column of Table II. This is passed through line 11 to hydrotreating operation 12 together with 5000 s.c.f.b. of hydrogen admitted through line 16. Hydrotreating is carried out at 650 F. and 500 p.s.i.g. (LHSV of 2.0) in the presence of 3.5% Ni and 15% Mo on alumina (American Cyanamide Aero HDS-3 catalyst); and the sulfur content is reduced from 100 p.p.m. to 1 p.p.m.

Hydrotreated, desulfurized charge paraiiinic hydrocarbon, shown as schematically leaving the hydrotreating operation through line 14, is passed to high pressure separation operation 15 wherein gases including hydrogen are separated and withdrawn through line 16. Hydrogen may be withdrawn from or added to the system through line 13.

The net product from the H.P. Separation is passed as a. hydrotreated desulfurized charge paraiiinic hydrocarbon stream through lines 17 and 18 to aromatizing operation 19, which in the preferred embodiment is a reforming operation. Aromatizing is carried out in the presence of 5300 s.c.f.b. of hydrogen admitted through line 20.

Aromatization is carried out at 950 F. and 15 p.s.i.g. (LHSV of 1.0) in the presence of 0.3% Pt and 0.3% Re on alumina (UOP-R-l6 catalyst). The product aromatic hydrocarbon stream leaving aromatization through line 21 is passed to low pressure separation operation 22 wherein gases including hydrogen are separated and withdrawn through line 23. Hydrogen may be withdrawn from or admitted to the system through line 24.

The net product (10,820 b.p.d.) from the LP. Separation operation has the following composition:

TABLE III Component: Vol. percent Hydrocarbons less than C5 36.0 Pentane 21.6 Benzene 19.4 Toluene 12.3 Other 18.9 RON Clear 92.2 RON +3cc 101.1

This product is passed as an aromatic hydrocarbon stream through line 25 to debutanizing operation 26.

In the debutanizing operation 26, 3600 b.p.d. of unconverted parain-olen stream is withdrawn through line 27 as overhead.

Aromatic concentrate bottoms at 950 F. and 15 p.s.i.g. are withdrawn from debutanizing operation 26 through line 28. This stream is passed through line 28 and line 29 to aromatics separation operation 30. In this embodi- 6 ment, the aromatic concentrate stream in line 28 is combined with a hydrogenated, thermally cracked naphtha stream to form a blended total charge stream in line 29 containing aromatic concentrate.

In aromatic separation operation 30, the charge aromatic concentrate is separated into a parain stream and an aromatic stream. In this embodiment, this may be carried out by contacting sulfolane solvent with the charge stream at 50 F. and 150 p.s.i.g. to yield, after recovery from the extract, 3815 b.p.d. of an aromatic stream removed through line 31. This stream may be passed to the gasoline pool.

The raflinate (containing unreacted parains) from aromatics separation operation 30 withdrawn through line 32, containing 4815 b.p.d. is combined with the debutanizer overhead stream in line 27 to form a combined parain stream in line 33.

The combined parat-lin stream in line 33 is passed to thermal steam cracking operation 34 wherein it is cracked in vapor phase at 1400 F. and 25 p.s.i.g. with a steam to hydrocarbon mole ratio of 5. Effluent is recovered in line 35.

The thermally steam cracked stream in line 35 is passed at 1400 F. and 25 p.s.i.g. to stripping operation 36 wherein it is separated into (i) as overhead 8550 b.p.d. of an olefin stream (withdrawn through line 37 at 200 F. and 25 p.s.i.g.) and (ii) as bottoms a thermally cracked naphtha stream withdrawn through line 38.

The thermally cracked naphtha (or dripolene) stream is passed through line 38 to hydrogenation operation 39 wherein it is hydrogenated in the presence of hydrogen.

Product hydrogenated, thermally cracked naphtha, is withdrawn through line 40. This stream is combined with the stream in line 28 as noted supra.

It will be apparent that in this processing technique, a light straight run naphtha may be upgraded into an aromatic stream of high octane number suitable for use in the gasoline pool and an olefin stream which is suitable for use in chemical operations.

Although this invention has been illustrated by reference to specic embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made which clearly fall within the scope of this invention.

We claim:

1. The method of upgrading a charge parainic hydrocarbon which comprises (a) aromatizing said charge paraiinic hydrocarbon in the presence of hydrogen and a noble metal supported catalyst thereby forming an aromatic hydrocarbon stream;

(b) debutanizing said aromatic hydrocarbon stream thereby forming (i) as overhead an unconverted paraffin stream and (ii) as bottoms an aromatic concentrate;

(c) separating said aromatic concentrate thereby forming (i) a separated parafiin stream and (ii) a separated aromatic stream;

(d) combining said overhead unconverted paraftin stream and said separated parain stream thereby forming a combined parain stream;

(e) thermally steam cracking said combined paraffin stream thereby forming a thermally cracked combined paraflin stream containing olens; and

(f) recovering said thermally cracked combined paraiin stream containing oleiins.

2. The method of upgrading a charge paranic hydrocarbon as claimed in Claim 1 wherein said charge parafiinic hydrocarbon is a C4 to C8 parainic hydrocarbon.

3. The method of upgrading a charge parafnic hydrocarbon as claimed in Claim 1 wherein said charge parafnic hydrocarbon is a naphtha.

4. The method of upgrading a charge parainic hydrocarbon as claimed in Claim 1 wherein said charge paraflinie hydrocarbon is hydrotreated to decrease the sulfur content prior to aromatizing.

5. The method of upgrading a charge paradinic hydrocarbon which comprises.

(a) aromatizing said charge parainic hydrocarbon in the 'presence of hydrogen and a noble metal supported catalyst thereby forming an aromatic hydrocarbon stream;

(b) debutanizing said aromatic hydrocarbon stream thereby forming (i) as overhead an unconverted paraffinic stream and (ii) as bottoms and aromatic concentrate;

(c) separating said aromatic concentrate thereby forming (i) a paraflin stream and (ii) an aromatic stream;

(d) combining said overhead unconverted parain stream and said overhead parain stream thereby forming a combined paraffin stream;

(e) thermally steam cracking said combined paran stream thereby forming a thermally cracked combined parain stream containing olefms;

(t) separating a thermally cracked naphtha stream from said thermally cracked product stream containing olens;

(g) hydrogenating said thermally cracked naphtha stream thereby forming a hydrogenated, thermally cracked naphtha stream; and

(h) separating an aromatic concentrate from said hydrogenated, thermally cracked naphtha stream.

6. The method of upgrading a charge paralnic hydrocarbon as claimed in Claim wherein said charge parafnic hydrocarbon is hydrotreated to reduce the sulfur content.

7. The method of upgrading a charge parafnic hydrocarbon as claimed in Claim S wherein said charge parafnic hydrocarbon is a light naphtha.

8. The method of upgrading a charge parainic hydrocarbon as claimed in Claim 5 wherein said aromatization is carried out in a reforming operation.

9. The method of upgrading a charge light naphtha parafnic hydrocarbonA which comprises:

(a) reforming said charge light naphtha parainic hydrocarbon at 500 F.-1l00 lF. in the presence of hydrogen and a supported catalyst containing a 8 Group VIII metal and a Group VIIB metal thereby forming an aromatic hydrocarbon stream;

(b) debutanizing said aromatic hydrocarbon stream thereby forming (i) as overhead an unconverted paratlinic stream containing olens and (ii)v as bottoms an aromatic concentrate containing benzene, toluene, and paraflins;

(c) separating said aromatic concentrate thereby forming (i) a separated paratlin stream and (ii) a separated aromatic stream;

(d) combining said overhead unconverted parain stream and said separated paraim'c stream thereby forming a combined paran stream;

(e) thermally steam cracking said combined paran stream at 1100 F.-1700 F. thereby forming a thermally cracked combined parain stream containing olens; and

(t) recovering said thermally cracked combined parafn stream containing olens.

10. The method of upgrading a charge light naphtha parainic hydrocarbon as claimed in Claim 9 including the further steps of stripping said thermally cracked combined paran stream containing olelins thereby forming a stripped thermally cracked naphtha stream;

hydrogenating said stripped thermally cracked naphtha stream thereby forming a hydrogenated, thermally cracked naphtha stream; and

separating an aromatic concentrate from said hydrogenated, thermally cracked naphtha stream.

References Cited UNITED STATES PATENTS 2,202,401 5/ 1940 Rosen 208-89 2,254,555 9/1941 Thomas 208-66 3,533,938 10/1970 Leas 208-89 3,714,022 1/1973 Stine 208-66 DELBERT E. GANTZ, Primary Examiner S. L. BERGER, Assistant Examiner U.S. Cl. X.R. 208-66 

